Materials used to repair defects in structural members should have certain characteristics. The material should be easily applied and should form high strength bonds to structural members made of varying materials. Particularly for outdoor repairs, the repair materials should be usable in many environments including environments having extremes of heat and cold and having the presence of substantial quantities of environmental water.
One particularly important end use for such repair compositions is in the recycle or reuse of railroad ties. Typically in the maintenance of the railroad right of way, the rails along with the tie plates and spikes are removed from railroad ties, which remain in the roadbed. If a new rail is to be spiked to the old tie, it is critical that the railroad tie spike holes be repaired prior to laying the new rail. The presence of spike holes in an old tie can cause problems since if a spike is driven into a portion of the tie near an old spike hole, the driving force of the spike can displace the spike from its intended location into an old hole, displacing the rail, tie plate and spike. In the instance that the spike is driven into an incorrect location substantial economic loss can result in repairing the misaligned rail. If a misaligned rail is not repaired, the defect can cause derailment or other problems. Further, the spike holes can be the source of structural weakness in the tie, allowing water to enter the core of the tie accelerating the degradation.
The use of polyurethane foam in filling spike holes in used railroad ties has come a long way, but still can present significant problems. The polyurethane foam compositions do not appear to consistently adhere to a spike hole with sufficient adhesion to prevent the accidental removal of the foam repair mass during the repair and subsequent mechanical rail installation. Further, most urethane foams of the prior art tended to foam uncontrollably in the presence of substantial environment moisture. Since moisture tends to accelerate the foaming properties of the urethane composition, the presence of water can cause too rapid of cell expansion resulting in a foam mass of low strength and low density that can result in the formation of an incomplete or unreliable repair of structural members.
Various polyurethane compositions and improvements have been suggested. However, there is still a substantial need in the art for repairing compositions that employ non-carcinogenic ingredients and that can be used to repair surface defects on structural components such as railroad ties to provide a repair mass having strong adhesion to the substrate structural member and strong pulling strength, which can be used in the presence of substantial quantities of environmental water and can be used in automatic application equipment in all temperatures.